In my Mac Pro review I lamented the state of 4K display support under OS X 10.9.0. In my conclusion I wrote: "4K display compatibility under OS X is still a bit like the wild west at this point". Compatibility was pretty much only guaranteed with the ASUS/Sharp 4K displays if you cared about having a refresh rate higher than 30Hz. Even if you had the right monitor, the only really usable resolution was 3840 x 2160 - which ends up making text and UI elements a bit too small for some users. Absent were the wonderful scaling resolutions that Apple introduced with its MacBook Pro with Retina Display. Well it looks like that won't be the case for long, last night I got reports (thanks Mike!) that the latest developer build of OS X 10.9.3 includes expanded support for 4K displays, 4K/60Hz support for rMBPs and scaled resolutions below 4K.

So, OS X is essentially the only desktop operating system with proper HiDPI support, right?

Having bought a Dell UP2418Q a couple of weeks ago I learned two things:

1) Windows 7's Hi-DPI support is a sad joke. And Office 365's Hi-DPI is also a sad joke. Pretty amazing how everything rolls a dice when selecting font sizes and how the uxtheme.dll engine doesn't support Hi-DPI, making all your buttons and windows look square and awful.

2) OS X does it flawlessly, except that you have to enable the feature with the Quartz debug development tool, which you can download from Apple if you have a developer account.

"OS X does it flawlessly, except that you have to enable the feature with the Quartz debug development tool, which you can download from Apple if you have a developer account.

I wouldn't say that's flawless. "
Okay, if you want to be really pedantic about it, yes, it isn't officially supported. But it actually works once enabled, unlike the officially supported things by the other platforms.

And from what I understand on the article, this thing is already fixed at Apple and will be automatically enabled in one of the next updates.

I call it flawless because it works 100% the same way as if you've ever seen a Mac laptop with retina display. I am personally yet to see any font or anything else get mangled on it. Contrast this with Microsoft bragging left and right on MSDN about their DPI awareness and then the OS itself (all the way down to the title bar of windows) can't even get it right.